1. Field of the Invention
The present invention relates to a rotary anode x-ray tube and a method of manufacturing a connecting rod arranged in the rotary anode x-ray tube.
2. Description of the Related Art
A conventional rotary anode x-ray tube has the following arrangement. A cathode electrode and an anode target are arranged in a vacuum vessel evacuated to a high degree of vacuum to oppose each other. The cathode electrode emits electrons. The anode target is fixed to a rotor through a connecting rod. The rotor is connected to a rotating shaft and is rotatably supported by a fixing portion through ball bearings. The rotor is rotated by a rotating magnetic field generated by a rotating magnetic field generator (not shown) arranged around the vacuum vessel. Upon rotation of the rotor, the anode target is integrally rotated.
In such a rotary anode x-ray tube, when electrons emitted from the cathode collide with the anode target, heat is generated together with x-rays. At this time, the anode target is heated to a temperature as high as 1,000.degree. C. or more.
When the anode target is heated to such a high temperature, the heat is conducted to the ball bearings by radiation and through the connecting rod, the rotating shaft, and the like. Of the ball bearings, those located near the anode target are especially heated to high temperatures. Under the circumstances, in x-ray tubes, one of the technical problems to be solved is how to lubricate ball bearings arranged in a high-temperature environment.
Especially in recent years, the use of high-intensity x-rays has been demanded in many cases in terms of x-ray applications. In order to satisfy this demand, the amount of collisions of hot electrons with an anode target must be increased to increase the amount of x-rays to be generated.
As described above, however, as the amount of x-rays is increased, lubrication of ball bearings becomes more difficult.
As has been described above, in the conventional rotary anode x-ray tube, with an increase in x-ray output, the temperatures of the ball bearings near the anode target are increased. This leads to difficulty in lubrication of the ball bearings.